Wednesday, March 21, 2012

Glacial Melt not all it's Cracked Up to be

"Even though previous GRACE based studies showed significant mass loss, the authors state that those measurements were in error—the outcome of “leakage” of readings from surrounding plains that was included by the Gaussian smoothing functions used. The excessive readings from the plains have been attributed to groundwater movement, not ice loss. They also dismiss any contribution from broad-scale tectonic uplift. In short, they found minimal ice loss from the glaciers of the Himalaya.

According to the report: “The GIC rate for 2003–2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period. The high mountains of Asia, in particular, show a mass loss of only 4 ± 20 Gt yr−1 for 2003–2010, compared with 47–55 Gt yr−1 in previously published estimates.” Bamber summarizes the article's findings this way:

First, the contribution of GICs (excluding the Antarctica and Greenland peripheral GICs) to sea-level rise was less than half the value of the most recent, comprehensive estimate obtained from extrapolation of in situ measurements for 2001–05 (0.41 ± 0.08 compared with 1.1 mm yr−1). Second, losses for the High Mountain Asia region — comprising the Himalayas, Karakoram, Tianshan, Pamirs and Tibet — were insignificant. Here, the mass-loss rate was just 4 ± 20 gigatonnes per year (corresponding to 0.01 mm yr−1 of sea-level rise), compared with previous estimates that were well over ten times larger. By a careful analysis, the authors discounted a possible tectonic origin for the huge discrepancy, and it seems that this region is more stable than previously believed.

The facts are in and the latest measurements clearly state that the Himalayan Glaciers are not melting at an abnormal rate. In fact, another new study, this time in Nature Geoscience, reports that annual groundwater fluxes for Nepal are larger in volume than the contribution from ice- and snowmelt. In “Impact of transient groundwater storage on the discharge of Himalayan rivers,” Christoff Andermann et al. report that a significant portion—perhaps as high as 50 percent—of the water discharged from the high mountains of Asia does not come from melting glaciers.